TORONTO — By the time Gaven Mayo got to a Montreal hospital after a bullet from a high-powered rifle ripped through his thigh, he had lost a massive amount of blood and by his own account was hovering between life and death.

But the 27-year-old from the Kahnawake First Nation attributes the fact that he didn't die to a simple device that can immediately arrest severe bleeding, giving surgeons time to repair the damage from traumatic injuries and saving lives that otherwise might have been lost.

"On the way to the hospital, I was still basically losing blood the whole way," he said Wednesday from his bed at McGill University Health Centre, where he has been recovering for the last six weeks while waiting for transfer to a rehabilitation centre. "After I arrived at the hospital, they said I had lost about 80 per cent of my blood."

Mayo declined to talk about how he got shot, but said the bullet passed through his leg, breaking his femur and ripping into his femoral artery — the major blood vessel in the leg.

He might have fatally bled out were it not for MUHC doctors using a newly adopted device, a balloon catheter that is inflated inside the aorta — the body's major artery — to halt all blood flow below the level of the diaphragm.

The device — known as the ER-REBOA catheter — is made of a thin flexible tube topped by a tiny inflatable balloon, which is fed into the femoral artery in the groin before being snaked into the aorta, in the same way an angioplasty catheter is introduced to open up blocked coronary arteries in people with heart disease.

"The job of the angioplasty balloon is to dilate the artery to get it to open up; this one is to just occlude the artery and block the flow (with) the balloon so you stop bleeding," said Dr. Andrew Beckett, an MUHC trauma surgeon who introduced the ER-REBOA device to the hospital.

Beckett said it takes only two minutes to get the catheter inserted and the balloon blown up, buying critical time for surgeons to get a patient to the operating room to repair a smashed organ or pelvic fracture, for example, that has caused a severe hemorrhage.

"You've got a window of about 45 minutes to an hour to get control of the bleeding and get the balloon (out)," he said. "These are very sick patients and in a lot of cases, if you don't get the balloon up, the patient can exsanguinate in five minutes."

The device is designed not only to stop bleeding in the lower half of the body, but to keep blood circulating to the brain, heart and lungs, he said, adding that once the balloon is inflated, a hemorrhaging patient's dangerously low blood pressure normalizes and their heart rate comes down.

"This is a treatment for hemorrhagic shock," said Beckett. "When you're having hemorrhagic shock, it's like a whole-body stroke or heart attack."

Beckett, a lieutenant-colonel in the Royal Canadian Medical Services and chief of general surgery and trauma for the Canadian military, was responsible for introducing the catheter to his hospital after hearing it discussed, especially in relation to U.S. combat injuries in Iraq and Afghanistan.

Once the device received Health Canada approval in late 2017, trauma doctors at MUHC began training in its use, said Beckett, who believes the Montreal hospital is the only one in Canada employing the hemorrhage-stopping tool so far.

He said U.S. doctors have used the catheter more than 2,000 times, resulting in "a lot of spectacular saves," including women who have experienced ruptured uteruses due to motor vehicle accidents. The Canadian military has also used it in Iraq.

The device has been employed on the battlefield to stave off bleeding in military personnel injured by IED blasts, allowing them to be stabilized enough to have them airlifted by helicopter to a field hospital.

"We're not ready for this in Canada yet, but some countries like the United Kingdom have put the catheter in pre-hospital environments and brought the patients to trauma centres," Beckett said.

Without the device, surgeons would have to crack open a patient's chest in order to clamp the aorta, an invasive procedure that is hard on patients and takes many weeks to heal.

"This is a much more elegant technique," he said. "By allowing us to rapidly control bleeding, (the catheter) saves lives, requires fewer blood transfusions and reduces morbidity associated with major open surgery."

Mayo, an iron worker who has a five-year-old daughter, believes using the catheter saved his life.

"To be honest, I believe I would be dead. I'm extremely grateful that they decided to use that."